Unanswered Question

hi! if i've given a range of ip from 152.226.224. 0 to with subnet mask of 255.255.240. 0 (/20) to our branch office.

Based on the range above, can i use the /23, /24 and etc subnet mask for larger number of subnets and smaller number of host per subnet? Can i create 22 subnets with 254 hosts?

What's the best practice for associating vlan to subnet?....what i meant here is that, any concern if i've multiple subnets within a vlan.


I have this problem too.
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Istvan_Rabai Sun, 10/12/2008 - 09:37

Hi David,

Yes you can divide this range to smaller subnets.

As to myself, I would do it the following way:

I would make a summarized picture about all the vlans and the number of hosts required in each vlan.

Then you will know what should be the number of ip addresses in each vlan.

You can select the mask size for a vlan based on the number of hosts the following way, example:

/24 mask = 8 host bits -> 2^8 -2 hosts = 254 hosts

/25 mask = 7 host bits -> 2^7 -2 hosts = 126 hosts

... etc

Let's say you have 40 hosts in a vlan.

Let's try a /27 mask:

5 host bits -> 2^5 -2 hosts = 30 hosts - isn't enough

Let's try a /26 mask:

6 host bits -> 2^6 -2 hosts = 62 hosts - enough.

So for the vlan with 40 hosts you can use a /26 mask.

You should do this for each vlan.

Then you can use largest vlans first to assign the ip address range and continue with the smaller vlans and finally end it with the vlans containing the smallest number of hosts.




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